The present invention relates generally to scheduling asynchronous transmissions and, more particularly, to scheduling asynchronous transmission, based upon timing offset information received for each of the subscriber units.
Wireless communication systems are commonly put in place to provide voice and data communications. These systems often are deployed in accordance with one or more of several well known standards, which have been developed to more readily allow for the interoperability of equipment produced by different manufacturers. While earlier systems were more principally concerned with voice communications, there has been a more recent effort to increasingly accommodate the transmission of data at ever increasing rates.
Several third generation standards have emerged, which attempt to accommodate the anticipated demands for increasing data rates. At least some of these standards support synchronous communications between the system elements, while at least some of the other standards support asynchronous communications. At least one example of a standard that supports synchronous communications includes CDMA2000. At least one example of a standard that supports asynchronous communications includes Wideband CDMA (W-CDMA).
While systems supporting synchronous communications can sometimes allow for reduced search times for handover searching and improved availability and reduced time for position location calculations, systems supporting synchronous communications generally require that the base stations be time synchronized. One such common method employed for synchronizing base stations includes the use of global positioning system (GPS) receivers, which are co-located with the base stations, that rely upon line of sight transmissions between the base station and one or more satellites located in orbit around the earth. However, because line of sight transmissions are not always possible for base stations that might be located within buildings or tunnels, or base stations that may be located under the ground, sometimes the time synchronization of the base stations is not always readily accommodated.
However, asynchronous transmissions are not without their own set of concerns. For example, the timing of uplink transmissions in an environment supporting autonomous scheduling by the individual subscribers can be quite sporadic and/or random in nature. While traffic volume is low, the autonomous scheduling of uplink transmissions is less of a concern, because the likelihood of a collision (i.e. overlap) of data from data being simultaneously transmitted by multiple subscribers is lower. Furthermore, in the event of a collision, there is spare bandwidth available to accommodate the need for any retransmissions. However, as traffic volume increases, the likelihood of data collisions (overlap) also increases. The need for any retransmissions also correspondingly increases, and the availability of spare bandwidth to support the increased amount of retransmissions correspondingly diminishes. Consequently, the introduction of explicit scheduling by a scheduling controller can be beneficial.
However even with explicit scheduling, given the disparity of start and stop times of asynchronous communications and more particularly the disparity in start and stop times relative to the start and stop times of different uplink transmission segments for each of the non-synchronized base stations, gaps and overlaps can still occur. Gaps correspond to periods of time where no subscriber is transmitting. Overlaps correspond to periods of time where multiple subscribers are transmitting simultaneously. Both gaps and overlaps represent inefficiencies in the usage of the available bandwidth and the management of rise over thermal (ROT), which if managed more precisely can lead to more efficient usage of the available spectrum resources and a reduction in the amount of rise over thermal (ROT).
Consequently, there is a need for a method and apparatus, which more precisely schedules asynchronous communications, in a manner that minimizes and/or eliminates gaps and overlaps thus reducing the rise over thermal (ROT).
The present invention provides a method of scheduling asynchronous transmissions for a plurality of subscriber units. The method includes receiving information associated with a plurality of subscriber units that have uplink data to transmit including uplink timing offset information associated with each of the subscriber units. Two or more subscriber units are then selected from a set of subscriber units having a timing offset differential, that is below a predetermined threshold, where the timing offset differential is the difference between the timing offset of a first subscriber unit and the timing offset of a second subscriber unit further selectively offset by a multiple of the transmission segment size, which minimizes the difference. The transmission segments, which are available for the uplink of data, are then allocated between the selected two or more subscriber units, which limits the number of transmission segments that have at least one of an overlap or a gap, and the amount of the at least one of overlap and gap.
In at least one embodiment, selecting two or more subscriber units includes selecting two or more subscriber units from a list of subscriber units having the highest scheduling priority.
In at least a still further embodiment, selecting two or more subscriber units having the highest scheduling priority includes selecting the subscriber unit from the list having the highest scheduling priority and selecting at least another subscriber unit from the list, which minimizes the offset differential.
In yet a still further embodiment, the power of a scheduled uplink transmission is based upon the indicated presence and the amount of any anticipated overlap.
The present invention further provides a scheduling controller for scheduling asynchronous transmissions in a plurality of subframes of one or more channels for a plurality of subscriber units. The scheduling controller includes a receiver for receiving information associated with a plurality of subscriber units, each having uplink data to transmit, the information including uplink timing offset information. The scheduling controller further includes a controller adapted for selecting two or more subscriber units having offset differentials, where the size of any one of an overlap and a gap is below a predetermined threshold, when adjacent transmission segments of a channel are allocated to different ones of the two or more subscriber units, and for allocating the transmission segments between the two or more selected subscriber units in accordance with the selection. The scheduling controller additionally includes a transmitter for transmitting to the selected two or more subscriber units the transmission segment allocations.
The present invention still further provides a subscriber unit including an uplink transmission controller for use in a subscriber unit for controlling the asynchronous transmission of uplink data. The uplink transmission controller includes a priority status module adapted for producing priority status information. The subscriber unit further includes a transmitter coupled to the priority status module for transmitting priority status information to a scheduling controller, and a receiver for receiving scheduling information. The uplink transmission controller further includes an uplink transmission timing module, coupled to the transmitter and the receiver, and adapted for selectively enabling the transmitter to asynchronously transmit the uplink data, in accordance with the received scheduling information.
These and other features, and advantages of this invention are evident from the following description of one or more preferred embodiments of this invention, with reference to the accompanying drawings.